This invention relates to inductive magnetic heads, and particularly to eliminating or reducing remnant magnetization and residual flux in the inductive magnetic head.
Inductive magnetic heads are commonly used in magnetic disk drives for writing data to magnetic disks. The magnetic head is operated by driving a write current through the inductive coil of the magnetic head, and reversing the direction of the current to reverse the magnetic field generated by the head. Field reversals in the head induce changes in magnetic dipoles on the disk to represent data. While several types of current driver circuits are commonly used to drive current in opposite directions through the coil, one common circuit is an H-bridge circuit. An H-bridge circuit employs four transistor switches operated to direct write current through alternating pairs of the switches of the circuit.
For optimal performance, it is necessary to periodically clear the inductive head by removing remnant magnetization and residual flux from the write head. Remnant magnetization and residual flux in the write head may polarize or bias the read head and erase data, even when the write head is supposed to be turned off.
Information is written by placing the inductive head in one of two states, which correspond to a 1 and a 0 in digital information. Usually, the inductive head is cleared by turning off the current into the head. However, as magnetic recording head dimensions have become smaller, the shape anisotropy of the magnetic pole may cause the head to stay magnetized even after the current is removed. This results in unintentional erasure of data on the disk.
It is known that applying an alternating and diminishing magnetic field to a magnetic material will diminish the total magnetic induction in the material to a substantially small amount, and sometimes to zero, resulting in the material becoming essentially demagnetized. This method, sometimes called AC erasure, has been used in the past in industrial applications, such as demagnetizing metal tools and erasing bulk quantities of magnetic tapes. Typically, the magnetic field applied to the target is diminished by moving the target farther away from the source of the magnetic field.
Therefore, it is desirable to find a way to clear a small inductive head that may stay magnetized even after current no longer flows to the inductive head. It is also desirable to find a simple and inexpensive way to clear an inductive head of remnant magnetization in an H-bridge circuit.